Summary

Sunspots consist of a dark central umbra and a brighter, filamentary surrounding penumbra (see the figure). What causes these features? Some clues come from the fact that the brightness is associated with energy loss by radiation; this provides a connection to the mechanisms responsible for the energy flow from the solar interior to its visible surface. On page 171 of this issue, Rempel et al. (1) report comprehensive numerical simulations that reproduce the structure and dynamics of sunspots. The results help to address fundamental questions about the fine structure of sunspots and their surroundings.